Interleukin-6 (IL-6) is a multi-function cytokine that is produced by a range of cells. It regulates immune responses, acute phase reactions, and hematopoiesis, and may play a central role in host defense mechanisms. It acts on a wide range of tissues, exerting growth-inducing, growth inhibitory, and differentiation-inducing effects, depending on the nature of the target cells. The specific receptor for IL-6 (IL-6R) is expressed on lymphoid as well as non-lymphoid cells in accordance with the multifunctional properties of IL-6. Abnormal expression of the IL-6 gene has been suggested to be involved in the pathogenesis of a variety of diseases, especially autoimmune diseases, mesangial proliferative glomerulonephritis, and plasmacytoma/myeloma (see review by Hirano et al., Immunol. Today 11, 443-449, 1990). Human myeloma cells are observed to produce IL-6 and express IL-6R. In experiments, antibody against IL-6 inhibited the in vitro growth of myeloma cells thus indicating that an autocrine regulatory loop is operating in oncogenesis of human myelomas (Kawano et al., Nature, 332, 83, 1988).
The IL-6R is present on the surface of various animal cells, and specifically binds to IL-6, and the number of IL-6R molecules on the cell surface has been reported (Taga et al., J. Exp. Med. 196, 967, 1987). Further, cDNA coding for a human IL-6R was cloned and a primary structure of the IL-6R was reported (Yamasaki et al., Science, 241, 825, 1988).
Mouse antibodies are highly immunogenic in humans and, for this reason, their therapeutic value in humans is limited. The half-life of mouse antibodies in vivo in human is relatively short. In addition, mouse antibodies can not be administered in multiple doses without generating an immune response which not only interferes with the planned efficacy but also risks an adverse allergic response in the patient.
To resolve these problems methods of producing humanized mouse antibodies were developed. Mouse antibodies can be humanized in two ways. The more simple method is to construct chimeric antibodies where the V regions are derived from the original mouse monoclonal antibody and the C regions are derived from suitable human antibodies. The resulting chimeric antibody contains the entire V domains of the original mouse antibody and can be expected to bind antigen with the same specificity as the original mouse antibody. In addition, chimeric antibodies have a substantial reduction in the percent of the protein sequence derived from a non-human source and, therefore, are expected to be less immunogenic than the original mouse antibody. Although chimeric antibodies are predicted to bind antigen well and to be less immunogenic, an immune response to the mouse V regions can still occur (LoBuglio et al., Proc. Natl. Acad. Sci. USA 84, 4220-4224, 1989).
The second method for humanizing mouse antibodies is more complicated but more extensively reduces the potential immunogenicity of the mouse antibody. In this method, the complementarity determining regions (CDRs) from the V regions of the mouse antibody are grafted into human V regions to create “reshaped” human V regions. These reshaped human V regions are then joined to human C regions. The only portions of the final reshaped human antibody derived from non-human protein sequences are the CDRS. CDRs consist of highly variable protein sequences. They do not show species-specific sequences. For these reasons, a reshaped human antibody carrying murine CDRs should not be any more immunogenic than a natural human antibody containing human CDRs.
As seen from the above, it is supposed that reshaped human antibodies are useful for therapeutic purposes, but reshaped human antibodies to the human IL-6R are not known. Moreover, there is no process for construction of a reshaped human antibodies, universally applicable to any particular antibody. Therefore to construct a fully active reshaped human antibody to a particular antigen, various devices are necessary. Even though mouse monoclonal antibodies to the human IL-6R, i.e., PM1 and MT18, were prepared (Japanese Patent Application No. 2-189420), and the present inventors prepared mouse monoclonal antibodies to the human IL-6R, i.e., AUK12-20, AUK64-7 and AUK146-15, the present inventors are not aware of publications which suggest construction of reshaped human antibodies to the human IL-6R.
The present inventors also found that, when the mouse monoclonal antibodies to the human IL-6R were injected into nude mice transplanted with a human myeloma cell line, the growth of the tumor was remarkably inhibited. This suggests that the anti-human IL-6 receptor antibody is useful as a therapeutic agent for the treatment of myeloma.